1. Field of the Invention
The present invention is related to a stent having a therapeutic substance for delivery to a target site in a body lumen and a method for manufacturing such a stent.
2. Background of the Invention
A wide range of medical treatments are known that utilize “endoluminal prostheses.” As used herein, endoluminal prostheses are intended to mean medical devices that are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring and artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation, arteries, such as those located within the coronary, mesentery, peripheral, or cerebral vasculature, veins, gastrointestinal tract, biliary tract, urethra, trachea, hepatic shunts, and fallopian tubes.
Various types of endoluminal prostheses are also known, each providing a structure for modifying the mechanics of the targeted luminal wall. For example, stent prostheses are known for implantation within body lumens for providing radial support to the wall tissue, which forms the various lumens within the body, and often more specifically within the blood vessels of the body.
To provide radial support to a blood vessel, such as one that has been widened by a percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty,” “PTA” or “PTCA”, a stent is implanted in conjunction with the procedure. Effectively, the stent is configured to overcome the natural tendency of the vessel walls of some patients to close back down (i.e. restenosis). As such, the stent acts as a scaffolding to resist the vessels tendency to close back down. Under this procedure, the stent may be collapsed to an insertion diameter and inserted into a body lumen at a site remote from the diseased vessel. The stent may then be delivered to the desired treatment site within the affected lumen and deployed, by self-expansion or balloon expansion, to its desired diameter for treatment.
In addition, it may be desirable to deliver a therapeutic substance to the treatment site in order to reduce the incidence of restenosis. Various drug eluting stents that simultaneously deliver a therapeutic substance to the treatment site while providing artificial radial support to the wall tissue are known. Therapeutic substances that may be delivered include antiplatelet agents, anticoagulant agents, antimicrobial agents, and antimetabolic agents. Endoluminal devices including stents are sometimes coated on their outer surfaces with a substance such as a drug releasing agent, growth factor, or the like. Stents have also been developed having a hollow tubular structure with holes or ports cut through the sidewall to allow drug elution from a central lumen, such as the stents disclosed in U.S. Pat. No. 5,891,108. Although the hollow nature of the stent allows the central lumen to be loaded with a drug solution that is delivered via the ports or holes in the sidewall of the stent, the hollow tubular structure may not have suitable mechanical strength to provide adequate scaffolding in the vessel.